The present invention relates to an image forming apparatus and more particularly to an image forming apparatus having a cooling device for effectively cooling a transfer material on which a toner image is fixed and an image is formed.
In recent years, an image forming apparatus has been miniaturized and speeded up, so that a problem arises that heat generated from a fixing device raises the temperature in the main body of the image forming apparatus and when discharging a transfer material, on which a toner image is fixed and an image is formed, into a paper receiving tray, a phenomenon of “inter-sheet adhesion” occurs often.
“Inter-sheet adhesion” is a phenomenon that when a toner image is fixed on a transfer material by the fixing device and is discharged onto the paper receiving tray, before the toner image on the transfer material is cooled and dried sufficiently, the next transfer material is overlaid on it, thus the toner image on the preceding transfer material is adhered to the print side of the next transfer material, or in a case of double side print, when fixing the second side (rear), the print side of the first side (surface) is also heated, so that when the print sides of the preceding transfer material and next transfer material make contact with each other, the toner images are adhered, or in a case of face-up paper discharge, even after the toner image of the preceding transfer material is cooled and dried, by the heat of the transfer material next discharged to the toner image surface, the toner image of the preceding transfer material discharged before is melted and adhered to the transfer material.
Therefore, when the phenomenon of “inter-sheet adhesion” occurs, even if the adhered sheets are peeled off thereafter by a user, traces are left on the image itself, and such a sheet can be hardly used, thus how to effectively cool a transfer material on which an image is formed in the image forming apparatus comes into a problem.
Therefore, conventionally, an art equipped with, on the upstream side of a fixing section in the conveying direction of a medium to be recorded (transfer material), a cooling roller for cooling by conveying a transfer material and absorbing the heat of the transfer material and a cooling section for cooling the cooling roller (for example, refer to Patent Document 1) and an art for arranging a blower and a duct for cooling a transfer material on both sides of the transfer material in the width direction (for example, refer to Patent Document 2) are disclosed, and an art for controlling the cooling capacity of the cooling section on the basis of the outside air temperature and humidity condition, print mode selection condition, and transfer material kind selection condition (for example, refer to Patent Document 3) and an art for installing a first cooling section for cooling by applying air inside the apparatus to the image forming side of a transfer material and a second cooling section for cooling by applying external air introduced from outside the apparatus to the rear of the transfer material and when conveying a transfer material via a reversible conveying path, controlling so as to stop the second cooling section when the first cooling section is in operation (for example, refer to Patent Document 4) are disclosed.
[Patent Document 1]                Tokkai 2004-109732 (Japanese Non-Examined Patent Publication)        
[Patent Document 2]                Tokkai 2003-66793 (Japanese Non-Examined Patent Publication)        
[Patent Document 3]                Tokkai 2004-45723 (Japanese Non-Examined Patent Publication)        
[Patent Document 4]                Japanese Patent JP-3347539        
However, Patent Document 1 and Patent Document 2 relate to a constitution for improving the cooling effect, though depending on the internal space of a small image forming apparatus, a cooling roller and a duct for sufficiently heightening the cooling effect cannot be adopted, and even if the control described in Patent Document 3 is adopted, it is difficult to be well adapted to every condition, and when the control of Patent Document 4 is adopted, a problem arises that the scale and control of the cooling device are complicated, thus the cooling effect cannot be heightened by a simple constitution.